My husband's motorcycle went up in flames in the pouring rain?

I would say there was a fuel leak and bad wiring.

He should have worn a jacket instead of a shirt.

Was the heavy rain accompanied by hail, then also lightning is present in a storm per definition and not all bolts of lightning are audible. Security camera's may have a few images a second and also there is this st Elmo's fire even though more present in rural environment and on marshland. Bikes are made from many conductive metals like aluminium and copper and have no "cage of Faraday" to keep electricity out. It isn't smart to leave it out in a thunderstorm. I rode in one at the end of races and celebration. I passed a flyover with many motorcycles standing there for shelter. I held my feet off the steps hoping for the best and read in the paper all those people with their bikes standing there were hit by lightning.

Weather cam sites may have evidence of lightning strikes during that day. Lightning occurs because the tumbling hail looses its outer static layer, falling trough warmer air or rain suddenly. Take a frozen cup out of the fridge and pour water in, sometimes one sees vapor elude swiftly from the surface. That is to the same effect. You spoke about heavy rain, this just may have been the hail leftover.

It was your ex husband

I'm just marking a place so I can come back to see what other will answer.

Watch the video, see where the fire begins. That's where your problem was.

Save the video the insurance company is going to want to see it.

Spontaneous aqueous combustion is exactly like spontaneous human combustion. Oh... I digress. Rain usually does nothing to properly wired motorcycles with good connectors and a secure insulated wiring harness (which you don't tell us about) because rain is generally pretty much like distilled water, which is an insulator. However, if hubby's bike is what's known as a POS, or rat-bike, there could be enough dried battery acid and road salt to create an ionic (conductive) solution when rain is added. It is a radical concept, but this is another reason to perform actual maintenance on, including cleaning, one's motorcycle.

need some more information on motorcycle- make. model, year. A few incidents of ignition switch shorts in rain and leaky fuel system have been reported on Mainland Chinese scooters and small motorcycles. Earlier limey classics rarely had fire problems in rain- but a few shorts in ignition mounted on top of headlight or center of top trees have been noted over the years, couple Harleys with center of gas tank ignitions left in rain got shorted- ignition switch had been damaged in theft attempt. Leaky carb from leaving petcock open and dribble of gasoline combine with short from wet can catch fire - riding lawn mower/(Craftsman) with some bad wiring on electric start caught fire , motorcycle- late 2 stroke Kaw or Yamaha laid down in rain and left laying had fire problem Janesville after couple hours- battery leak, gas leak, rain blamed for shorting along with dropped from side stand in dirt letting fall over in rain.

Who leaves a perfectly good motorcycle sitting out in pouring rain?

It's punishment from the motorcycle GOD.

possible i guess